1. A nova is a star that brightens abruptly by a large factor. Some novae may become as much as tens of thousands of times brighter than our Sun. The rapid brightening is caused by a runaway thermonuclear explosion on the surface of a white dwarf star; a small star that packs about as much mass as our Sun into a volume the size of Earth. The white dwarf accumulates the hydrogen that fuels the nova outburst from an ordinary star that is a close companion. The explosion ejects mass from the surface of the white dwarf, enriching space with heavier elements produced during the thermonuclear explosion. Although novae have been known since ancient times, and astrophysicists have understood the cause of a nova explosion since the middle of the last century, important puzzles still remain. Over the past several years, spacecraft observations have revealed that at least some novae emit very high-energy gamma radiation. This was unexpected and is still mysterious. Some novae also may be progenitors of Type Ia supernovae, which have significant implications for cosmology. The Principal Investigator will conduct extensive scientific analyses of the atlas of observational data he has accumulated for 83 novae over the past 14 years. This research will address several key questions about novae. The results of the investigations constitute the Intellectual Merit of this project. The Broader Impacts stem from the PI's proposed involvement of undergraduates and high-school students directly in the research. He points out that since 1991, five of the high-school students he has supervised have been semi-finalists in the Intel Science Talent Search. The PI will also collaborate with the American Association of Variable Star Observers (AAVSO) to enhance the experiences of participating amateur observers.
2. Nova eruptions are caused by thermonuclear runaways at the degenerate base of an accreted H layer on a white dwarf. The hydrogen layer is accumulated by mass transfer from a close binary companion star. During outburst, a nova increases in brightness, in some cases reaching tens of thousands of times the luminosity of the Sun. A nova explosion ejects as much one ten-thousandth of a solar mass from the white dwarf into the interstellar medium, enriching it in heavier elements produced in the nuclear burning event. During the past several years, the Fermi Gamma Ray Observatory has discovered that some novae emit high-energy gamma radiation; the origin of these emissions is still not well understood. Some novae also may be the precursors of Type Ia supernovae, which have important implications for cosmology. In order to address several key questions about these eruptive variables, the Principal Investigator will conduct exhaustive scientific analyses of the atlas of high-cadence photometric and spectroscopic data he has accumulated for 83 novae over the past 14 years. The results of these investigations constitute the Intellectual Merit of this project. The Broader Impacts stem from the PI's proposed involvement of undergraduates and high-school students directly in the research. He points out that since 1991, five of the high-school students he has supervised have been semi-finalists in the Intel Science Talent Search. The PI will also collaborate with the American Association of Variable Star Observers (AAVSO) to enhance the experiences of participating amateur observers.
